HOLGATE SCHOOL
 ENVIRONMENTAL EDUCATION

 

'VIRTUAL VISITS'

BURBAGE VALLEY, DERBYSHIRE
Burbage valley is 8km north-west of Sheffield. The valley is drained by Burbage brook, a tributary of the R. Derwent. The valley has been carved through two different types of rock - 'millstone grit' and 'shale'. Within this small area we can explore the range of factors which affect the work of rivers.

1.

Burbage brook rises on a moorland plateau. Beneath the surface are impermeable gritstone rocks, so this moorland is very wet. The poor drainage means that vegetation does not rot easily, and a layer of peat has formed over the surface.

2.

In the upper valley the concave slopes are formed with millstone grit at the top and shale beneath. Around the 'rim' of the valley is a crag of millstone grit known locally as an 'edge'. Millstone grit is a resistant rock which has distinctive bedding and jointing planes. Frost shattering in the 'ice age' expanded these cracks and divided the rock into blocks. Some of the blocks of weathered rock have tumbled from the crags, and rolled or slid down the slopes. This is called mass movement.

3.

In most of the valley Shale is the rock which forms the valley floor. It is a soft rock, with numerous thin beds. It is easily broken by weathering and easily eroded by the river. It is impermeable and the waterlogged beds of shale are likely to cause landslides. In this view we see the orange colouring in the water which tells us that the shale is being chemically weathered, and the iron compounds are being washed into the river.

4.

In the upper part of the valley the river flows over resistant beds of gritstone, The bed of the stream is steep, making it fast-flowing. The energy of the fast flowing water allows it to transport large boulders (in times of flood) as 'bedload'. At this point the valley sides are steep and the floor of the valley is narrow. Boulders are tumbled down the steep sides of the valley by Mass Movement.

5.

In the central part of the valley, the width increases. The valley 'opens out'. The skyline is still dominated by gritstone capped hills. The shale beneath has been smoothed and the angle of the valley sides reduced. Coniferous woodland has been planted in this part of the valley. Elsewhere the rough grazing, of coarse grass and bracken, is food for a few sheep. This area is not economically favourable for farming.

6.

In the middle section of the valley the river meanders. At the outside of the bends the river undercuts the hillside and landslides occur(see below), bringing rock and soil debris into the river. At the inside of the bend is a flatter area, built up over time by deposition.

7.

Here we see how open the middle section of the valley has become. In the distance the plateau of Burbage Edge is fringed with cliffs, formed of resistant millsone grit. The slopes beneath the 'edges' are littered with gritstone blocks which are being carried downhill by mass movement. Weathered shale has been formed into soil, which has become vegetated. Close to the river are steeper slopes created by landslides.

8.

The flat topped hill called Higger Tor lies to the west of the valley. Notice the difference in slope angle between the resistant gritstone and the less resistant shale. Notice also the rough vegetation which grows on the poor badly drained soils.

9.

This is 'Toads Mouth bridge' which carries the main road across Burbage brook. Downstream from the bridge the valley opens out even more.

10.

In the lower section of the valley the river is wider, and contains more water. The gradient of the bed is gentler. The valley sides are gentler. Soils are deeper and better developed so the grass is better. Mixed woodland is the natural vegetation of this area.

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